Technician Question of the Week T3B08 Spectrum Limits

The radio spectrum is parsed into several broad categories of frequency ranges. These broad bands of frequencies are designated by descriptive names from Extremely Low Frequency (ELF)to Extremely High Frequency (EHF). Nestled between these extreme bands are several others, including three bands that are most popular for amateur radio: High Frequency (HF), Very High Frequency (VHF), and Ultra High Frequency (UHF). Let’s consider one important aspect of radio signal transmission where this frequency categorization can be useful to us.

As described in the HamRadioSchool.com Technician License Course book Chapter 5, Signal Propagation, frequency propagation characteristics can be grouped and described roughly along these broad regions of the RF spectrum.

The relatively low frequencies of the HF band (10-meter to 80-meter amateur bands) are notable for their refraction by the electrically charged layers of the ionosphere that promote RF signal “skip” over the horizon and around the globe. The HF region of the spectrum is from 3 – 30 MHz.

The VHF frequency bands (6-meter, 2-meter, & 1.25-meter) are known for their occasional E-layer ionosphere skip or “Sporadic-E,” for their occasional over-the-horizon travel by tropospheric ducting during temperature inversions in the lower atmosphere, and for reflection by aurora and by meteor ionization trails. The 2m band is also commonly used for satellite communications because it is not usually refracted significantly by the ionosphere. Except for the less common conditions mentioned above, VHF is usually considered to have RF line-of-sight propagation. (See Ham Radio 101: How Far Can I Talk With My Radio?) The VHF region of the spectrum is from 30 – 300 MHz.

The relatively high UHF frequencies are virtually never affected significantly by the ionosphere or other atmospheric phenomena, making them perfect for punching through the atmosphere into space for satellite contacts. Like VHF in common conditions, UHF is almost always RF line-of-sight propagation. The UHF region of the spectrum is from 300 – 3000 MHz.

Notice in the available responses to question T3B08 there is a tricky distracter answer: 30 – 300 kHz. That’s kilohertz rather than megahertz. Don’t pounce too quickly on the correct numerical values only to miss this question due to selecting incorrect units. All questions of this type in the Technician pool have correct answers with megahertz units.

The answer to Technician pool question T3B08, “What are the frequency limits of the VHF spectrum?” is B: 30 to 300 MHz.